X-Ray Beam Properties and Interactions

For an electron to be removed from its shell, the filament electron's kinetic energy must be equal to or greater than the binding energy of the electron it interacts with.
Example: If a filament electron has 50 keV of kinetic energy and strikes a K-shell electron with a binding energy of 69.5 keV, it will not remove the K-shell electron.
The result of insufficient energy is heat, which occurs 99% of the time.

Brems is a German word meaning "breaking" or "slowing down."
In a Brems interaction, the filament electron misses all the electrons on the anode side.
The attraction between the filament electron and the nucleus causes the filament electron to slow down, change direction, and lose kinetic energy.
This loss of kinetic energy results in the emission of a Brems photon.
The energy of the Brems photon is determined by subtracting the energy the filament electron has when leaving the atom from the energy it had when entering.
$E<em>{photon} = E</em>{entering} - E_{leaving}$
Example: A filament electron enters an atom with 100 keV, passes near the nucleus, and leaves with 30 keV. The resulting Brems photon has an energy of 70 keV.
- Incoming electron: 100 keV
- Outgoing electron: 30 keV
- Brems photon: 70 keV
100
ormal{keV} - 30
ormal{keV} = 70
ormal{keV}

Most photons produced with a tungsten target are Bremsstrahlungs photons.
Statistically, only K-shell characteristic interactions have enough energy to be useful in X-ray imaging. Other shell interactions are too weak and are filtered out.
Filament electrons are more likely to miss the orbital electrons due to constant motion and empty space within the atom.

The important properties of an X-ray beam for a radiographer are quantity and quality.
Filtration affects the X-ray beam.

Filtration involves using a material (usually aluminum or an aluminum equivalent) to absorb low-energy X-ray photons from the beam.
Types of Filtration:
- Inherent Filtration: Natural filtration from the X-ray tube components (e.g., oil bath, lead lining, target window).
- Added Filtration: Additional filtration placed in the tube head assembly (e.g., 2 mm aluminum sheet between the target window and the collimator).
- Total Filtration: Combination of inherent and added filtration.
- Compensating Filter: Adjusts for variations in patient thickness or density (e.g., wedge filter for a foot, boomerang filter for a neck).
  - Placed after the X-ray tube or collimator on the bottom of the anatomical part of interest.

Quantity: The total number of X-ray photons in the beam.
Affected by technique (mAs and kVp) and distance from the tube.
Quantity is associated with radiation dose; the further from the tube, the less radiation received.
Increasing quantity increases the dose delivered.
Adjustments in quantity are made via mAs.

Beam quantity varies as the square of the ratio of the change in kVp.
Doubling kVp increases intensity/quantity by a factor of four.
A 15% increase in kVp is equivalent to doubling the mAs.
$Quantity <br />\neq kVp^2$
kVp and mAs are technical factors used in balance.
Beam quantity is strongly affected by changes in kVp because kVp provides the kinetic energy.
High kVp and low mAs are preferred for X-rays.

Quantity varies inversely as the square of the distance.
The intensity of the beam is inversely proportional to the square of the distance.
$Intensity <br />\neq \frac{1}{Distance^2}$
Filtration decreases the overall total amount of radiation by filtering out low-energy photons.

Quality: Penetrating power or strength.
Penetration refers to the amount of X-rays that pass through the body and reach the image receptor.
Photons reaching the image receptor create dark shades; areas where light or clear indicate absorption.
Quality is affected by:
- kVp: As kVp increases, the beam's ability to penetrate matter increases.
- Filtration: Removes lower-energy photons, increasing the overall average energy.

Primary Beam: The X-ray beam that exits the X-ray tube before interacting with the patient.
Remnant Beam: The beam that exits the patient after interaction.